The subject of the present invention is a geared motor unit, particularly for driving vehicle equipment, such as window lifters, sunroofs, etc, and of the type including a rotor equipped with a rotor shaft and a reduction gearbox which contains a gearwheel in mesh with a worm belonging to the rotor shaft and capable of driving an output member.
Geared motor units of this type are normally equipped with means for adjusting the axial play between one end of the rotor shaft and the wall of the reduction gearbox. The axial play in the driveling mounted in the geared motor unit is due to the combination of dimensional spreads on the various parts on assembly (shaft, endstop, box, etc.) which, placed end to end, are not as long as their housing.
Previously the axial play has been compensated for by manually using a screw housed in the end of the reduction gearbox facing the rotor shaft hole and which is immobilized by an adhesive which also provides sealing. Such a method of adjustment is lengthy to perform, expensive, and increases the overall cost of manufacture of the geared motor unit.
It is also a known practice (see U.S. Pat. No. 5,169,245) to achieve automatic compensation for the axial play in the driveling of the geared motor unit using a coil spring resting in an axial housing of the end of the reduction gearbox and a system of end stops designed to limit the compressive axial loading experienced by the coil spring to a predetermined value. This limitation is achieved by a shoulder on the inside of the wall of the reduction gearbox and against which a piston inserted between the end of the rotor shaft and the coil spring abuts.
The Patent Abstract of Japan Vol. 018 No. 297 dated Jun. 7, 1994 also discloses a geared motor unit in which an end stop, fixed by welding to one end of the reduction gearbox, eliminates any axial play between the rotor shaft and the wall of the reduction gearbox.
These devices for compensating for the axial play have a drawback which lies in the fact that they are not able to eliminate the troublesome noise of the rotor shaft caused by a change in the direction of rotation.